Electrochemical conversion cells, commonly referred to as fuel cells, produce electrical energy by processing reactants, for example, through the oxidation and reduction of hydrogen and oxygen. A typical polymer electrolyte fuel cell comprises a polymer membrane (e.g., a proton exchange membrane (PEM)) with catalyst layers on both sides (catalyst coated membrane (CCM)). The catalyst coated PEM is positioned between a pair of gas diffusion media layers (DM), and a cathode plate and an anode plate are placed outside the gas diffusion media layers. The components are compressed to form the fuel cell.
In order to form a CCM, the electrode ink can be deposited directly on the PEM, or it can be deposited on a decal substrate and transferred to the PEM.
Depending on the fuel cell design, catalyst coated diffusion media (CCDM), in which the catalyst is coated on the DM rather than the PEM, sometimes have advantages over CCM. Gas diffusion media in PEM fuel cells are normally composed of a layer of a conductive porous substrate, such as carbon fiber paper or carbon cloth, with a microporous layer (MPL) thereon. The MPL normally contains carbon powders and hydrophobic fluoropolymers. Traditionally, CCDM are prepared by coating a catalyst containing ink directly on the gas diffusion layer, more precisely onto the MPL.
Typically, in the fuel cell, the operating conditions are not uniform from the stack inlet to the stack outlet. For example, relative humidity (RH) increases from the inlet to the outlet, while O2 partial pressure decreases.
Therefore, there is a need for adjusting the electrode/MEA properties along the flow direction.